medium-sized gimlet may be sunk into the pattern at each end and then by lifting upon the two at the same moment, the pattern can be "drawn" or lifted without trouble, as every care has been taken to prevent the sand mixture from adhering to the pattern. With metal patterns a hole is drilled into the pattern and threaded, and a rod with threads to match is then screwed into same and thus it "draws" without injury to the mold. The blocks used to mold the inlets for mortar or gates are removed, and the two sections of mold are then ready to place together again and the concrete poured into same. In the case of simple bas-relief designs the cope is not required, as the lower section of flask makes the entire face plate or sand mold; where a block or body is required to the stone to be cast, a box form is erected around the sand mold and the concrete poured into same; completing the cast or work. CHAPTER V MAKING MOLDS FROM CLAY, PLASTER, OR CONCRETE PATTERNS IN securing a pattern for the mold it is not always possible to have it of such material, or in such condition that it can be divided where we wish; hence we must construct the flask so as to correct the deficiency of the pattern. Again, with a mold to be made from a clay model, that has cost a large amount of work to complete and has many lines and under-cuttings, the worker should not risk making the mold in the usual manner, as failure may mean the loss of clay model as well as mold; but by having the flask so divided that it is an easy matter to remove the pattern from the sand, as well as to remove the work from the mold; when cast in concrete, the most intricate or unusual shaped pattern may be molded with success. In making molds from clay, plaster, or concrete patterns, as well as from wood patterns, the surface of pattern must be protected from the moisture in the sand mixture. With the wood pattern this moisture is apt to warp the lumber, when the pattern is used more than once or twice, but by coating with oil several times, so as to fill the pores of the wood with the oil, and then varnishing the pattern with any good varnish, the wood pattern is unaffected by the moisture. With the clay or plaster pattern the surface requires a coating that will give it a hard finish; not only impervious to the moisture in the sand but to enable the clay or plaster to withstand the pressure exerted by the tamping of the sand in mold; if this is not done any material as plastic as modeling clay would be pressed entirely out of shape by this pressure. There are several ways of securing the desired result of which the most simple is to coat with shellac; several coats are carefully applied to the surface, allowing each one to dry well before applying the next; this makes a hard coating over the entire surface, conforming to every line and curve with exactness; thus securing a protective surface that will preserve the model while making the mold. 16 Another method is to coat lightly with shellac and then over this coat with thin glue; placing one coat upon the other until a shell is secured of a thickness of " to "; this is valuable where the pattern presents a very broad surface, as in the center it is apt to be depressed by the tamping of the sand, but with a hard protective coating to hold the material in pattern exactly in place, the sand may be tamped solidly without injury to the softest of pattern material, as well as being entirely unaffected by the moisture in the material for mold. In large and intricate patterns, that will require separate cores, it is often valuable to color the shellac or varnish so that you can quickly locate on pattern the point where these cores will be placed; thus if the pattern is coated with the ordinary shellac, the core points may be painted with a red color mixed with the shellac. Or two parts of a pattern may be |